A corporation keeping track of assets (e.g., desks, chairs, computers) will often try to accomplish this by means of assets tags. Each asset tag is adhesively secured to an asset, and bears a tracking number or bar code or both. Carrying out an inventory is a tedious process, requiring a lot of people and a lot of time. It is unworkable to carry out a building-wide inventory more often than about once a year.
Given the problems with numbered or bar-coded tags, many investigators have tried to keep track of assets using radio tags such as RFID tags. But locating radio tags in a large or multi-room space is not easy. Among the reasons why this is not easy are the following.
Range. Most radio tags work only if the reader is immediately adjacent to the tag. For example, many RFID tags can only be read at a distance of inches. Among the RFID tags that can be read from more than a few inches away, many can only be read from more than a few inches away in the special case where a high-gain antenna is pointed directly at the tag.
Collisions and area reads. Most radio tags simply respond when powered. If many such tags are nearby to each other, all within a reading area of a reader, what generally happens is that all the tags respond simultaneously, and the collision often means that few or none of the tags can actually be read. Complicated collision-avoidance and disambiguation schemes can be attempted but such schemes often do not work well.
Detuning. Many radio tags many recent RFID tags, get detuned if they are nearby to large pieces of metal or other conductors. With many prior-art systems, a detuned tag may be treated as a tag that does not exist, as it will fail to respond to queries.
Skin depth. Many radio tags, especially many recent RFID tags, simply cannot be reached if there are intervening objects blocking the RF signals. The RF signals are unable to pass back and forth through the intervening objects.
Some approaches that have attempted to overcome these problems are prodigiously expensive.
It would thus be extremely desirable to have a reasonably priced system that would permit area reads, over a substantial range (many feet), robust against detuning, and effective even in the face of intervening objects.